Method for determining frequency components in a vehicle crash

ABSTRACT

A method for determining frequency components present in a particular type of vehicle crash for which it is desirable to actuate a passenger restraint system in a vehicle of a predetermined class of vehicles is disclosed. The method comprises the steps of providing a time domain vibratory electric signal that is responsive to and that includes frequency component values indicative of a vehicle crash, crashing a vehicle of the predetermined class under at least one condition in which it is not desirable to actuate the vehicle passenger restaint system and recording an associated vibratory electric signal, crashing a vehicle of the predetermined class under at least one condition in which it is desirable to actuate the vehicle passenger restraint system, recording an associated vibratory electric signal, and performing a frequency domain transform function on the time domain recorded signals so as to identify frequency components for the electric signals recorded both crash conditions. The method further comprises the steps of comparing the frequency components for the crash conditions for which it is not desirable to actuate the passenger restraint system against the frequency components for the crash conditions for which it is desirable to actaute the passenger restraint system, and identifying frequency components present in crash conditions in which it is desirable to actuate the passenger restraint system and not present in the crash conditions in which it is not desirable to actuate the passenger restraint system.

This is a continuation of copending application(s) Ser. No. 07/432,128filed on Nov. 3, 1989 now abandoned.

TECHNICAL FIELD

The present invention is directed to an actuatable passenger restraintsystem for a vehicle and is particularly directed to a method fordetermining frequency components that are present in particular,predetermined types of vehicle crashes.

BACKGROUND

Actuatable passenger restraint systems for vehicles are well known inthe art. One particular type of actuatable passenger restraint systemincludes an inflatable air bag mounted within the passenger compartmentof the vehicle. Each air bag in the vehicle has an associated,electrically actuatable ignitor, referred to as a squib. Such systemsfurther include an inertia sensing device for measuring the decelerationof the vehicle. When the inertia sensing device indicates that thevehicle is decelerating at a rate above a predetermined amount, anelectric current of sufficient magnitude and duration is passed throughthe squib to ignite the squib which, in turn, ignites a combustible gasgenerating composition or pierces a container of pressurized gas,thereby inflating the air bag.

Many known inertia sensing devices used in actuatable passengerrestraint systems are mechanical in nature. Such devices are typicallymounted to the vehicle frame and include a pair of mechanicallyactuatable switch contacts and a resiliently biased weight. The weightis arranged such that when the vehicle is decelerated, the weightphysically moves relative to its mounting. The greater the rate ofdeceleration, the further the weight moves against the bias force. Theswitch contacts are mounted relative to the biased weight such that,when the weight moves a predetermined distance, the weight moves over oragainst the switch contacts causing them to close. The switch contacts,when closed, connect a squib to a source of electrical energy sufficientto ignite the squib.

Still other known actuatable passenger restraint systems for vehiclesinclude an electrical transducer or accelerometer for sensing vehicledeceleration. Such systems include a monitoring or evaluation circuitconnected to the output of the transducer. Such transducers provided anelectric signal having a value indicative of the vehicle's rate ofdeceleration. The monitoring circuit processes the transducer outputsignal. One typical processing technique is to integrate the transduceroutput signal. If the output of the integrator exceeds a predeterminedvalue, an electrical switch is actuated to connect electrical energy tothe squib. One example of such a system is disclosed in U.S. Pat. No.3,870,894 to Brede, et al., ("the '894 patent").

The '894 patent discloses a system which includes an accelerometer, anevaluation circuit connected to the accelerometer, and an ignitioncircuit or squib connected to an output of the evaluation circuit. Theaccelerometer includes a piezoelectric transducer that provides anelectrical output signal having a value indicative of the vehicledeceleration. The evaluation circuit includes an integrator electricallycoupled to the output of the accelerometer through an amplifier. Theoutput of the integrator is an electrical signal having a valueindicative of the integral of the deceleration signal. A trigger circuitis connected to the output of the integrator. When the output of theintegrator reaches a predetermined value, the trigger circuit actuates atime delay circuit. The time delay circuit begins to time out apredetermined time period. After the time period is timed out, the airbag ignitor is energized.

It has been discovered that it is not desirable to inflate a vehicle airbag under all types of crashes to which the vehicle is subjected. It isnot desirable, for example, to inflate the air bag during a low speed,"soft crash." The determination as to what occurrences fall within thedefinition of "soft crash" is dependent upon various factors related tothe type of vehicle. If, for example, a large vehicle traveling eightmiles per hour hits a parked vehicle, such a crash would be considered a"soft crash" that would not require the air bag to inflate to protectthe vehicle passengers. The vehicle seat belts alone would be sufficientto provide passenger safety. During such a "soft crash," a typicalaccelerometer would provide an output signal indicating a rapiddeceleration is occurring. In an actuatable passenger restraint systemmade in accordance with the '894 patent, the air bag would be inflatedas soon as the predetermined speed differential occurred and the timedelay circuit timed out.

Another type of electronic control arrangement for an actuatablepassenger restraint system is disclosed in U.S. Pat. No. 4,842,301. The'301 patent discloses an air bag actuation circuit that monitors theacoustic emissions produced during crushing of a vehicle of a typehaving a welded, unit body structure with a pair of frame side railsextending longitudinally from the front of the vehicle to the back ofthe vehicle. Two acoustic vibration sensors, in accordance with the '301patent, are secured as close as possible to the front of respective siderails. The output of each of the sensors is connected to a band passfilter with a frequency range of 200 KHz to 300 KHz so as to excludelower frequency components. The outputs of the bandpass filters areconnected to envelope detectors. The outputs of the envelope detectorsare connected to comparators. Once the level of the acoustic vibrationsin the pass band frequency exceed a value set by the comparatorreference, the air bag is actuated.

SUMMARY OF THE PRESENT INVENTION

The present invention provides a method for distinguishing betweendifferent types of vehicle crashes by determining which frequencycomponents are present in a signal from a deceleration sensor upon theoccurrence of a vehicle crash condition. Once the frequency componentsare known, an actuatable passenger restraint system can be electricallycontrolled to inflate the system's air bag only upon the occurrence of aparticular type of crash, one that requires the use of the air bag forprotection of the vehicle passengers.

In accordance with the present invention, a method is provided fordetermining frequency components present in a particular type of vehiclecrash for which it is desirable to actuate a passenger restraint systemin a vehicle of a predetermined class of vehicles. The method comprisesthe steps of, (a) providing a time domain vibratory electric signal thatis responsive to and that includes frequency component values indicativeof a vehicle crash, (b) crashing a vehicle of the predetermined classunder at least one condition in which it is not desirable to actuate thevehicle passenger restraint system, and (c) recording the vibratoryelectric signal for the vehicle crash of step (b). The method alsoincludes the steps of (d) crashing a vehicle of the predetermined classunder at least one condition in which it is desirable to actuate thevehicle passenger restraint system, (e) recording the vibratory electricsignal for the vehicle crash of step (d), and (f) performing a frequencydomain transform function on the time domain recorded signals so as toidentify frequency components for the electric signals recorded for thecrashes of steps (b) and (d). The method also includes the steps of (g)comparing the frequency components for the crash of step (d) against thefrequency components for the crash of step (b), and (h) identifyingfrequency components present for the crash of step (d) and not presentfor the crash of step (b).

In accordance with another aspect of the present invention, a method isprovided for designing filter circuits for an actuatable vehiclepassenger restraint system having a deceleration sensor that provides anelectric signal having frequency component values indicative of aparticular type of crash of a predetermined class of vehicles for whichit is desirable to actuate the passenger restraint system. The filtercircuits monitor when the frequency components indicative of theparticular type of vehicle crash are present and provide a signalindicative thereof. The method comprises the steps of (a) crashing avehicle of the predetermined class under at least one condition in whichit is not desirable to actuate the vehicle passenger restraint system,(b) recording the signal from the deceleration sensor for vehicle crashin step (a), (c) crashing another vehicle of the particular class underat least one condition in which it is desirable to actuate the vehiclepassenger restraint system, (d) recording the signal from thedeceleration sensor for vehicle crash in step (c), (e) performing atransform function on each of the signals recorded in steps (b) and (d),and (f) designing the filter circuits to pass those frequenciesdetermined to be present in step (e) only for the crash in step (c).

In accordance with a preferred embodiment of the present invention amethod for is provided for designing filter circuits for an actuatablevehicle passenger restraint system having a deceleration sensor thatprovides an electric signal having frequency component values indicativeof a particular type of crash of a predetermined class of vehicles forwhich vehicle crash type it is desirable to actuate the passengerrestraint system and having frequency component values indicative ofother types of vehicle crashes for which it is not desirable to actuatethe passenger restraint system, said filter circuits monitoring when thefrequency components indicative of the particular type of vehicle crashare present and providing a signal indicative thereof, said methodcomprising the steps of: (a) crashing a vehicle of the predeterminedclass under a plurality of conditions in which it is not desirable toactuate the vehicle passenger restraint system; (b) recording the signalfrom the deceleration sensor for each of the vehicle crashes in step(a); (c) crashing a vehicle of the predetermined class under a pluralityof conditions in which it is desirable to actuate the vehicle passengerrestraint system; (d) recording the signal from the deceleration sensorfor each of the vehicle crashes in step (c); (e) performing a transformfunction on each of the signals recorded in steps (b) and (d); (f)designing the filter circuits to pass those frequencies determined to bepresent in step (e) only for crashes in step (c); and (g) designing thefilter circuits to pass those frequencies determined to be present instep (e) only for crashes in step (a).

In accordance with the preferred embodiment, the step of performing atransform function includes the step of performing a Fourier transform.The step of designing includes the step of designing a bandpass filterthat passes the electric signals having frequency componentscorresponding the frequency components present in the signals recordedin step (d). The step of designing the filter circuits includes the stepof determining a frequency band 3 db down of each side of a determinedcenter frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent to those skilled in the art to which the present inventionrelates from a reading of the following detailed description ofpreferred embodiments with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic diagram of an apparatus for controlling actuationof a vehicle restraint system in accordance with the present invention;

FIG. 2 is a schematic diagram of the accelerometer assembly shown inFIG. 1;

FIG. 3 is a schematic diagram of a band-pass filter and envelopedetector shown in FIG. 1;

FIG. 4 is a graphical representation of the output of the accelerometerassembly when the vehicle is subjected to a non-deployment, barriercrash;

FIG. 5 is a graphical representation of the Fourier transform of theoutput signal shown in FIG. 4;

FIG. 6 is a graphical representation of the output of the accelerometerassembly when the vehicle is subjected to a long velocity change,deployment crash condition;

FIG. 7 is a graphical representation of the Fourier transform of theaccelerometer output shown in FIG. 6;

FIG. 8 is a schematic block diagram showing a hardware arrangement toobtain empirical data in accordance with the present invention;

FIG. 9 is a flow diagram showing the control process for determiningfrequency components during vehicle crashes;

FIG. 10 is a graphical representation of the output signal from theaccelerometer during a non-deployment barrier crash overlaid with theoutput of the summation circuit shown in FIG. 1 and with the output ofthe bandpass filter shown in FIG. 1 but off-set for clarity;

FIG. 11 is a graphical representation of the Fourier transform of thebandpass Filter output shown in FIG. 10;

FIG. 12 is a graphical representation of the output of the accelerometerassembly overlaid with the output of the summation circuit shown in FIG.1 and with the output of the bandpass filter shown in FIG. 1 but off-setfor clarity;

FIG. 13 is a graphical representation of the Fourier transform of thebandpass filter output shown in FIG. 12;

FIG. 14 is an apparatus for controlling actuation of a passengerrestraint system made in accordance with another embodiment of thepresent invention; and

FIG. 15 is a schematic of the negative envelope detectors shown in FIG.14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 schematically depicts an apparatus 20 for use in controllingactuation of an air-bag restraint system. An accelerometer assembly 22is securable to the vehicle and provides a vibratory electric outputsignal having frequency components indicative of the type of crashcondition to which the vehicle is subjected. The output 24 is connectedto an integrator circuit 26 of a type well known in the art. The output24 of the accelerometer assembly 22 is also connected to the inputterminal 28 of a boost circuit 30. The boost circuit 30 includes abandpass filter 32 designed for passing frequency components within aparticular frequency band that are present in the output signal 24 ofthe accelerometer assembly 22. An output 34 of the bandpass filter 32 isconnected to an envelope detector circuit 36. An output 38 of theintegrator 26 and an output 40 of the envelope detector 36 are bothconnected to a summing circuit 42.

An output 44 of the summing circuit 42 is connected to one input 46 of acomparator 48. Another input 50 of comparator 48 is connected to ajunction 52 of a voltage dividing network including series connectedresistors 54, 56 connected between a source of electrical energy V andelectrical ground.

An output 58 of the comparator 48 is connected a one-shot 60. Theone-shot 60 provides a pulse signal 62 having a predetermined timeduration when the comparator senses that the output voltage 44 isgreater than the voltage value at the junction 52. This pulse indicatesthat the vehicle is subjected to a crash condition for which it isdesired to actuate the passenger restraint system. For the purposes ofexplanation, the passenger restraint system discussed herein is an airbag.

The output 62 of the one-shot 60 is connected to an electric switch 64,such as a field effect transistor ("FET"). The switch 64 is connected inseries with a squib 66 between a source of electrical energy V andelectrical ground. The one-shot pulse length is selected so as to insurethat electrical current is supplied to the squib 66 for a duration thatexceeds the manufacturer's specified minimum time period to insureactuation. Upon firing of the squib 66, the air bag is deployed.

The accelerometer assembly 22 includes an accelerometer transducer 68that outputs a vibratory electric signal 70 having frequency componentsindicative of a particular type of vehicle crash condition. The output70 of the accelerometer transducer 68 is connected to an amplifier 72that amplifies the signal 70 and provides the output signal 24.

Referring to FIG. 2, the accelerometer 68 includes a mass 74 suspendedby a cantilever support arrangement 76 secured to a housing 78. Thehousing 78 is securable to the vehicle. Four variable resistors 80 aremounted to the cantilever support arrangement. The resistors 80 areelectrically connected in a Wheatstone bridge configuration betweenelectrical ground and a source of electrical energy V.

When the mass 74 of the accelerometer 68 moves relative to its housing78, as happens during a vehicle crash, the resistance values of theresistors 80 change. Because of the Wheatstone bridge configuration, avoltage variation occurs across terminals 82, 84 which is indicative ofthe movement of the mass 74. Such a transducer or accelerometer isavailable commercially from ICSensors, 1701 McCarthy Blvd., Milpitas,Calif. 95035 under Model No. 3021.

The bridge resistors 80 are connected to amplifier 72 which provides theoutput signal 24 having a value indicative of the movement of the mass74. Specifically, terminal 82 is connected to a non-inverting input 86of an operational amplifier ("op amp") 88. The output 90 of op amp 88 isconnected to its inverting input 92 through feedback resistor 94.Terminal 84 is connected to a non-inverting input 96 of an op amp 98.The output 100 of the op amp 98 is connected to its inverting input 102through a feedback resistor 104. The inverting input 92 of op amp 88 andthe inverting input 102 of op amp 98 are connected together through avariable resistor 106.

The output 90 of the op amp 88 is also connected to the non-invertinginput 108 of op amp 110 through a resistor dividing network includingresistors 112, 114. A filter capacitor 116 is connected between thejunction of resistors 112, 114 and electrical ground. The output 100 ofop amp 98 is also connected to the inverting input 118 of op amp 110through a resistor 120. The output 122 of op amp 110 is connected to itsinverting input 118 through parallel connected resistor 124 andcapacitor 126.

If the resistors 94, 104, 112, 114, 120, and 124 have equal resistancevalues, designated as R, and if the value of the variable resistor 106is designated Rvar, the gain "G" of the amplifier 72 is given by:

    G=(1+(2R/Rvar))

The boost circuit 30 of FIG. 1 is shown in detail in FIG. 3. Theband-pass filter 32 includes the input terminal 28 which is connected tothe output 24 of the amplifier 72. The amplitude of the input signal isdivided by series connected resistors 140, 142. The junction of theresistors 140, 142 is connected to an inverting input 144 of an op amp146 through a capacitor 148. The non-inverting input 150 of the op amp146 is connected to electrical ground. The output 152 of the op amp isconnected to the inverting input 144 through a resistor 154. Thejunction of the resistors 140, 142 is connected to the output 152 of theop amp 146 through a capacitor 156.

When selecting the component values for the band-pass filter 32, afrequency F is selected half way between the values f1 and f2 whichdefine a frequency band limit for which the filter is to pass. A value Qis set equal to the value F divided by the frequency band width that is3 db down from the peak value of the frequency F. The value of resistor140 is designated R140. All other resistor values are similarlydesignated, i.e., RXXX where XXX is the resistor number from thedrawing. The value of capacitor 148 is designated C148. The value ofother capacitors are similarly designated, i.e., CXXX where XXX is thecapacitor number from the drawing. The frequency F can be expressed as:

    F=(1/2π)[(1/(R154×C148×C156))×((1/R140)+(1/R142))].sup.1/2

The gain G of the band-pass filter 32 can be express as:

    G=R154/[R140×(1+(C156/C148))]

The values of the resistors are then determined by: ##EQU1##

The envelope detector circuit 36 includes a diode 160 having its anode162 connected to the output 152 of the bandpass filter 32. The cathode164 of the diode 160 is connected to parallel connected resistor 166 andcapacitor 168.

Referring to FIG. 4, the output 24 of the accelerometer assembly 22 isgraphically depicted with amplitude on the y-axis and time on the x-axisfor a non-deployment vehicle crash. The rough appearance to the graph ofthe output signal 24 is due to the vibrations of the mass 74 during thevehicle crash. The output 38 of the integrator 26 is also depicted. FIG.5 graphically depicts the Fourier transform of the accelerometer signaldepicted in FIG. 4. Amplitude is on the y-axis and frequency is on thex-axis. The Fourier transform transforms the time domain output signalfrom the accelerometer assembly 22 into a frequency domain signal. TheFourier transform provides an indication as to what frequency componentsare present in the time domain signal. It has been discovered that theoutput 24 of the accelerometer assembly 22 includes particular frequencycomponents that identify the particular type of vehicle crash to whichthe vehicle is subjected.

As can be seen in FIG. 5, no frequency components are present betweenfrequency values f1 and f2. By no frequency components being present, itis meant that frequency components between values f1 and f2 haveamplitudes less than a predetermined value or have no significant valuerelative to the amplitude of the frequency components that are presentelsewhere in the spectrum. Referring to FIGS. 6 and 7, the time domaingraph and the frequency domain graph of a deployment crash are depicted,respectively. The output 38 of the integrator 24 is also depicted. Ascan be seen in FIG. 7, the deployment crash does have frequencycomponents present between the values f1 and f2.

It has been further discovered that if one could determine for aparticular type of vehicle of concern which frequency components arepresent during a deployment crash and are not present during anon-deployment crash, one could continuously monitor the output 24 forthose frequency components and actuate the air bag upon detection ofthose frequencies.

Referring to FIG. 8, an apparatus 180 is shown for determining frequencycomponents that are provided by the accelerometer assembly 22 attachedto a vehicle during different types of crash conditions, i.e.,non-deployment crashes and deployment crashes. A deployment crash is onein which it is desirable to deploy the air bag. A non-deployment crashis one in which it is not desirable to deploy the air bag.

The accelerometer assembly 22 is exactly as described above. The output24 of the accelerometer assembly 22 is connected to an analog-to-digital("A/D") converter 182. A crash sensor enable circuit 184 is connected tothe output 24 of the accelerometer assembly 22 and to the A/D converter182. The crash sensor enable circuit 184 monitors the accelerometersignal 24. When the magnitude of the signal 24 is greater than apredetermined value, the crash sensor enable circuit 184 enables the A/Dconverter to begin conversion. The converted data is stored in a memorydevice 186.

After test data is acquired and stored, the data is subsequentlyprocessed by a digital transform processor 190. The digital transformprocessor 190 may take one of several forms, such as a Fouriertransformer, a cosine transformer, or one of other several types knownin the art. The output 192 of the transformer 190 is connected to amicrocomputer 194. The microcomputer 194 correlates the particulars ofthe crash parameters, i.e., whether the crash was under deploymentconditions or non-deployment conditions, with the determined frequenciesdetected by the digital transform processor. The microcomputer 194 thenidentifies which frequency components are present during a deploymentcrash condition and not present during a non-deployment crash condition.Alternatively, the output of the digital transform processor can bedisplayed on an oscilloscope. From the display of the transform data forboth a deployment and a non-deployment crash condition, it can beascertained by an observer which frequencies are present during adeployment crash condition that are not present during a non-deploymentcondition.

It is contemplated that the accelerometer assembly 22, the A/D converter182, the crash sense enable circuit 184, and the memory 186 would be onboard the vehicle being tested. The digital transform processor 190 andmicrocomputer 192 would be out board of the vehicle. After the vehicleis crashed and the data is stored in the memory 186, the digitaltransform processor 190 could then be connected to the memory 186 forfurther processing and analysis.

FIG. 9 depicts a flow chart of the control process in accordance withthe present invention for obtaining the frequency components fordeployment and non-deployment crashes for a vehicle. It is contemplatedthat the control process will be followed for each make and model ofvehicle. This is necessary because the frequency components for the sametype of crash condition may vary dependent upon the vehicle type orclass. Step 250 starts the control process. In step 252, a vehicle ofthe particular type is crashed at non-deployment conditions, such as aeight mile per hour barrier crash. The accelerometer assembly outputsignal 24 for the non-deployment crash condition run in step 252 isrecorded in step 254. The output signal 24 from the accelerometerassembly 22 during such a non-deployment crash condition are depicted inthe graph of FIG. 4. In step 256, a Fourier transform is performed onthe non-deployment crash data recorded in memory 184. The transform datais depicted in the graph of FIG. 5. As can be seen from the graph ofFIG. 5, no significant frequency components are present for thefrequency band between frequency f1 and frequency f2.

In step 258, the same type of vehicle is crashed at deploymentconditions such as a low speed pole crash. The accelerometer assemblyoutput signal 24 for the deployment crash condition run in step 258 isrecorded in step 260. The output signal 24 from the accelerometerassembly 22 during such a deployment crash condition is depicted in thegraph of FIG. 6. In step 262, the Fourier transform is performed on thestored deployment crash data. The transform data is depicted in thegraph of FIG. 7. As can be seen from the graph of FIG. 7, significantfrequency components are present for the frequency band betweenfrequency f1 and frequency f2. Based upon this information, a band passfilter is designed in step 264 for the frequency band so as to passsignals present between frequency f1 and frequency f2. The componentvalues for the band pass filter are determined according to theequations discussed above.

Referring to FIGS. 4 and 6, the output 38 of the integrator 26 is shownfor both a non-deployment crash condition (FIG. 4) and for a deploymentcrash condition (FIG. 6). FIG. 10 depicts the same non-deployment crashas depicted in FIG. 4. Also depicted in FIG. 10 is the output 34 of thebandpass filter 32 and output 44 of the summing circuit 42, which is thesum of the output of the integrator circuit 26 and the boost circuit 30.The output of the bandpass filter 32 is shown offset on the y-axis forpurposes of clarity. A threshold value Vt is selected which, for allnon-deployment crash conditions, will be greater than the value of theoutput 44. Running non-deployment crash conditions with the boostcircuit is depicted in FIG. 9 at step 266. The Fourier transform of thebandpass filter output is shown in FIG. 11. Between frequencies f1 andf2, there are few frequency components present. These frequencycomponents are insignificant in magnitude as compared to the output ofthe bandpass filter during a deployment crash condition. Selecting thevalue of a threshold value Vt is depicted in step 268 of FIG. 9. Basedupon the selected value Vt, the resistive values of resistors 54, 56 areselected so that the voltage at the junction 52 is equal to Vt. Themethod of determining which frequency components are present duringnon-deployment and deployment crash condition, the designing of thebandpass filter based upon this information, and the selection of afiring threshold is completed in step 270 of FIG. 9.

Referring to FIG. 12, the output 24 of the accelerometer assembly 22 isdepicted during the same deployment crash condition shown in FIG. 6. Theoutput 34 of the bandpass filter 32 and the output 44 of the summingcircuit 42 are also depicted. FIG. 13 depicts the Fourier transform ofthe bandpass filter 32 for this deployment crash occurrence. There arefrequency components present between frequencies f1 and f2 having asignificant magnitude relative to the values shown in FIG. 11. It shouldbe appreciated that, as a result of the boost circuit 30, the output 44of the summing circuit 42 rises very rapidly as compared to the outputof the integrator circuit alone.

The apparatus schematically shown in FIG. 1, which is made in accordancewith the present invention, permits the distinction between a deploymentcrash condition having a long velocity change pulse and a non-deploymentlow speed barrier crash condition to better control the actuation of theair bag. Also, the arrangement, in accordance with the presentinvention, acts to filter out certain occurrences for which it is notdesirable to actuate the air bag. For example, if the vehicle wassubject to a high frequency hammer blow, those frequencies would befiltered out by the bandpass filter. The integrator output would notchange from a hammer blow due to the short duration of the occurrence ofthe event.

Referring to FIG. 14, another embodiment of the present invention isschematically depicted. An accelerometer assembly 22 having an output 24is provided and is the same as described above. The output 24 of theaccelerometer assembly 22 is connected to deployment circuitry 300 andnon-deployment circuitry 302. It has been discovered that when aparticular type of vehicle is subjected to a plurality of differenttypes of non-deployment crash conditions, certain frequency componentsare present that are not present during deployment crash conditions.Conversely, it has been discovered that when a particular type ofvehicle is subjected to a plurality of different types of deploymentcrash conditions, certain frequency components are present that are notpresent during non-deployment crash conditions. Based on this discovery,it has been determined that control of the passenger restraint systemcan be controlled by evaluating a plurality of discrete frequency bandsduring a vehicle crash. Control of the air bag is responsive to whetherthere are more deployment frequency components present or morenon-deployment frequency components present.

The deployment circuitry 300 includes a plurality of bandpass filters320, 322, 324, 326 all connected to the output 24 of the accelerometerassembly 22. The frequencies to be passed by the bandpass filters of thedeployment sensors are determined using the empirical techniquedescribed above by crashing the same type of vehicle at severaldifferent deployment conditions and noting which frequency componentsare present for deployment conditions, but not present fornon-deployment crash conditions. Positive envelope detectors 330, 332,334, 336, are respectively connected to the bandpass filters 320, 322,324, 326. The outputs of the envelope detectors 330, 332, 334, 336 areconnected to a summing circuit 340.

The non-deployment circuitry 302 include a plurality of bandpass filters350, 352, 354, 356 all connected to the output 24 of the accelerometerassembly 22. The frequencies to be passed by the bandpass filters of thenon-deployment sensors are determined using the empirical techniquedescribed above by crashing the same type of vehicle at severaldifferent non-deployment conditions and noting which frequencycomponents are present for non-deployment conditions but not present fordeployment crash conditions. Negative envelope detectors 360, 362, 364,366, are respectively connected to the bandpass filters 350, 352, 354,356. The outputs of the envelope detectors 360, 362, 364, 366 areconnected to the summing circuit 340.

FIG. 15 schematically depicts a negative envelope detector of the typecontemplated for use in the non-deployment circuitry 302. The negativeenvelope detector includes a diode 370 having its cathode 372 connectedto the output of a non-deployment bandpass filter. The anode 374 of thediode 370 is connected to a parallel combination of resistor 376 andcapacitor 378. The anode 374 is connected to the summing circuit 340.

When a signal is provided from the accelerometer assembly 22 as during avehicle crash, frequencies that may be present indicative of anon-deployment condition or of a deployment condition are passed by theappropriate bandpass filters. The resultant summation is filtered by afilter circuit 380. The output of the filter 380 is connected to aninput 386 of a comparator 388. The other input 390 of the comparator 388is connected to a reference voltage Vt as was described above. Theoutput 392 of the comparator 388 is connected to a one-shot 60 asdescribed above. When the presence of deployment frequency componentsminus the presence of any non-deployment frequency components exceedsthe value Vt, the squib is actuated.

As should be appreciated, the embodiment of FIG. 14 reduces the need foror, if the number of deployment bandpass filters and the non-bandpassfilters is sufficient enough, eliminates the need for an integrator. Thearrangement shown in FIG. 14, although not shown as being connected inparallel with an integrator, can be so connected.

It is contemplated that all the band pass filters for the differentembodiments described in this specification would be passing frequencycomponents of less than 3 KHz.

This invention has been described with reference to preferredembodiments. Modifications and alterations may occur to others uponreading and understanding this specification. For example, the boostcircuit shown in FIG. 1 could be replaced with a deletion circuit thatwould monitor the accelerometer output signal for the presence offrequency components indicative of a non-deployment condition. Thisdeletion circuit would subtract from the integrator signal to prevent afalse indication of a deployment condition. Also, the preferredembodiment has been described with regard to actuation of an air bagrestraint system. The method and apparatus of the present invention isjust as applicable to other passenger restraint system. For example, theactuation signal can be used to lock a seat belt in a lockable seat beltsystem or to actuate a pretensioner for a seat belt retractor in a seatbelt system. It is our intention to include all such modifications andalterations insofar as they come within the scope of the appended claimsand the equivalents thereof.

Having fully described our invention, we claim:
 1. A method for determining frequency components present in a particular type of vehicle crash for which it is desirable to actuate a passenger restraint system in a vehicle of a predetermined class of vehicles, said method comprising the steps of:(a) mounting a first accelerometer in a first vehicle of the predetermined class, said first accelerometer providing a time domain vibratory electric signal in response to a vehicle crash, said vibratory electric signal having frequency component values functionally related to the type of vehicle crash; (b) crashing said first vehicle of the predetermined class under a condition in which it is not desirable to actuate the vehicle passenger restraint system; (c) recording said vibratory electric signal for said vehicle crash of step (b); (d) mounting a second accelerometer in a second vehicle of the predetermined class, said second accelerometer providing a time domain vibratory electric signal in responsive to a vehicle crash, said vibratory electric signal having frequency component values functionally related to the type of vehicle crash; (e) crashing said second vehicle of the predetermined class under a condition in which it is desirable to actuate the vehicle passenger restraint system; (f) recording said vibratory electric signal for said vehicle crash of step (e); (g) identifying frequency components for said electric signals recorded for the crashes of steps (b) and (e); (h) comparing said identified frequency components for said crash of step (e) against said identified frequency components for said crash of step (b); and (h) identifying which frequency components were present for said crash of step (e) and were not present for said crash of step (b).
 2. A method for designing filter circuits for an actuatable vehicle passenger restraint system having a deceleration sensor that provides an electric signal that is responsive to, and has frequency component values indicative of, a plurality of different types of crashes of a predetermined class of vehicles, said filter circuits monitoring when frequency components are present which are indicative of a particular type of vehicle crash and for which it is desirable to actuate the passenger restraint system and providing a signal indicative thereof, said method comprising the steps of:(a) mounting a first deceleration sensor to a first vehicle of the predetermined class, said first deceleration sensor providing an electric signal having frequency components indicative of a particular type of crash condition; (b) crashing said first vehicle of the predetermined class under a condition in which it is not desirable to actuate the vehicle passenger restraint system; (c) recording the signal from said first deceleration sensor for said vehicle crash of step (b); (d) mounting a second deceleration sensor to a second vehicle of the predetermined class, said second deceleration sensor providing an electric signal having frequency components indicative of a particular type of crash condition; (e) crashing a second vehicle of the predetermined class under a condition in which it is desirable to actuate the vehicle passenger restraint system; (f) recording signal from said second deceleration sensor for said vehicle crash of step (e); (g) performing a frequency domain transform function on said signals recorded in steps (c) and (f); and (h) designing the filter circuits to pass those frequencies determined to be present in step (g) only for said crash in step (e).
 3. The method of claim 2 wherein the step of performing a transform function includes the step of performing a Fourier transform.
 4. The method of claim 2 wherein the step of designing includes the step of designing a bandpass filter that passes electric signals having frequency components corresponding to the frequency components present in the signals recorded in step (d).
 5. The method of claim 4 further including the step of determining a frequency band 3 db down of each side of a determined center frequency.
 6. A method for designing filter circuits for an actuatable vehicle passenger restraint system having a deceleration sensor that provides an electric signal that is responsive to, and has frequency component values indicative of, a plurality of different types of crashes of a predetermined class of vehicles, said filter circuits monitoring when frequency components are present which are indicative of a particular type of vehicle crash and for which it is desirable to actuate the passenger restraint system and monitoring when frequency components are present which are indicative of other types of vehicle crashes and for which it is not desirable to actuate the passenger restraint system, and providing a signal indicative thereof, said method comprising the steps of:(a) crashing individual vehicles of the predetermined class, having an associated deceleration sensor mounted thereto, under a plurality of conditions in which it is not desirable to actuate the vehicle passenger restraint system; (b) recording the signals from said associated deceleration sensors for said vehicle crashes of step (a); (c) crashing individual vehicles of the predetermined class, having an associated deceleration sensor mounted thereto, under a plurality of conditions in which it is desirable to actuate the vehicle passenger restraint system; (d) recording signals from said associated deceleration sensors for said vehicle crashes of step (c); (e) performing a frequency domain transform function on each of said signals recorded in steps (b) and (d); (f) designing the filter circuits to pass those frequencies determined to be present in step (e) only for crashes in step (c); and (g) designing the filter circuits to pass those frequencies determined to be present in step (e) only for crashes in step (a).
 7. The method of claim 6 wherein the step of performing a transform function includes the step of performing a Fourier transform.
 8. The method of claim 6 wherein the step of designing includes the step of designing a bandpass filter that passes electric signals having frequency components corresponding the frequency components present in the signals recorded in step (d).
 9. The method of claim 8 further including the step of determining a frequency band 3 db down of each side of a determined center frequency. 